Seismic magnitude scales in the context of "2004 Indian Ocean earthquake and tsunami"

Anydros (Greek: Άνυδρος) is an uninhabited Greek islet in the municipality of Santorini, which is a group of islands in the Cyclades. It is north of the island Anafi, and southwest of Amorgos. It is sometimes called Greek: Αμοργοπούλα, romanized: Amorgopoúla. The island hosts a seismometer, part of the Greek national network, installed in 2025. An earthquake fault located near Anydros was the source of the 1956 Amorgos earthquake that registered 7.6 on the Richter scale and caused widespread damage on Amorgos and the island of Santorini, where dozens died.A second 7.5 quake and a 30-meter tsunami followed.

There were hundreds of minor earthquakes of up to magnitude 5 in an area around Anydros at the beginning of February 2025, causing concern in Santorini and causing more than half the population to leave the island. The seismic activity was attributed to tectonic plate movements rather than volcanism, and it was thought that it could last weeks.

An earthquake occurred in the province of Sichuan, China at 14:28:01 China Standard Time on May 12, 2008. Measuring at 8.0 M_s (7.9–8.3 M_w), the earthquake's epicenter was located 80 kilometres (50 mi) west-northwest of Chengdu, the provincial capital, with a focal depth of 19 km (12 mi). The earthquake ruptured the fault for over 240 km (150 mi), with surface displacements of several meters. The earthquake was also felt as far away as Beijing and Shanghai—1,500 and 1,700 km (930 and 1,060 mi) away, respectively—where office buildings swayed with the tremor, as well as Bangkok, Thailand and Hanoi, Vietnam. Strong aftershocks, some exceeding 6 M_s, continued to hit the area up to several months after the main shock, causing further casualties and damage. The earthquake also caused the largest number of geohazards ever recorded, including about 200,000 landslides and more than 800 quake lakes distributed over an area of 110,000 km (42,000 sq mi).

Over 69,000 people lost their lives in the quake, including 68,636 in Sichuan province. 374,176 were reported injured, with 18,222 listed as missing as of July 2008. The geohazards triggered by the earthquake are thought to be responsible for at least one third of the death toll. The earthquake left at least 4.8 million people homeless, though the number could be as high as 11 million. Approximately 15 million people lived in the affected area. It was the deadliest earthquake to hit China since the 1976 Tangshan earthquake, which killed at least 242,000 people, and the strongest in the country since the 1950 Assam–Tibet earthquake, which registered at 8.6 M_w. It was the 4th deadliest natural disaster of the decade. It is the 18th deadliest earthquake of all time. The economic loss of the earthquake was 845.1 billion yuan (US$130 billion). On November 6, 2008, the central government announced that it would spend 1 trillion yuan (about US$146.5 billion) over the next three years to rebuild areas ravaged by the earthquake, as part of the Chinese economic stimulus program.

The Philippines lies within the zone of complex interaction between several tectonic plates, involving multiple subduction zones and one large zone of strike-slip, all of which are associated with major earthquakes. Many intraplate earthquakes of smaller magnitude also occur very regularly due to the interaction between the major tectonic plates in the region. The largest historical earthquake in the Philippines was the 1918 Celebes Sea earthquake with a magnitude of M_w 8.3.

Mount St. Helens (known as Lawetlat'la to the local Cowlitz people, and Loowit or Louwala-Clough to the Klickitat) is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States. It lies 52 miles (83 km) northeast of Portland, Oregon, and 98 miles (158 km) south of Seattle. Mount St. Helens takes its English name from that of the British diplomat Alleyne FitzHerbert, 1st Baron St Helens, a friend of explorer George Vancouver who surveyed the area in the late 18th century. The volcano is part of the Cascade Volcanic Arc, a segment of the Pacific Ring of Fire.

The Mount St. Helens major eruption of May 18, 1980, is currently the most economically destructive volcanic event in U.S. history. Fifty-seven people were killed and 200 homes, 47 bridges, 15 miles (24 km) of railways, and 185 miles (298 km) of highway were destroyed. A massive debris avalanche, triggered by a magnitude 5.1 earthquake, caused a lateral eruption that reduced the elevation of the mountain's summit from 9,677 to 8,363 ft (2,950 to 2,549 m), leaving a 1-mile-wide (1.6 km) horseshoe-shaped crater. The debris avalanche was 0.6 cubic miles (2.5 km) in volume. The 1980 eruption disrupted terrestrial ecosystems near the volcano. By contrast, aquatic ecosystems in the area greatly benefited from the amounts of ash, allowing life to multiply rapidly. Six years after the eruption, most lakes in the area had returned to their normal state.

The Alpine Fault is a geological fault that runs almost the entire length of New Zealand's South Island, being about 600 km (370 mi). long, and forms the boundary between the Pacific plate and the Australian plate. The Southern Alps have been uplifted on the fault over the last 12 million years in a series of earthquakes. However, most of the motion on the fault is strike-slip (side to side), with the Tasman district and West Coast moving north and Canterbury and Otago moving south. The average slip rates in the fault's central region are about 38 mm (1.5 in) a year, very fast by global standards. The last major earthquake on the Alpine Fault was in about 1717 AD with a great earthquake magnitude of M_w8.1± 0.1. The probability of another one occurring before 2068 was estimated at 75 percent in 2021.

The Modified Mercalli intensity scale (MM, MMI, or MCS) measures the effects of an earthquake at a given location. This is in contrast with the seismic magnitude usually reported for an earthquake.

Magnitude scales measure the inherent force or strength of an earthquake — an event occurring at greater or lesser depth. (The "M_w" scale is widely used.) The MMI scale measures intensity of shaking, at any particular location, on the surface. It was developed from Giuseppe Mercalli's Mercalli intensity scale of 1902.

The 1976 Tangshan earthquake (Chinese: 唐山大地震; pinyin: Tángshān dà dìzhèn; lit. 'Great Tangshan earthquake') was a M_w 7.6 earthquake that hit the region around Tangshan, Hebei, China, at 19:42:55 UTC on 27 July (03:42:55, 28 July local time). The maximum intensity of the earthquake was XI (Extreme) on the Mercalli scale. In minutes, 85 percent of the buildings in Tangshan collapsed or were rendered unusable, all services failed, and most of the highway and railway bridges collapsed or were seriously damaged. The official count stated 242,469 deaths, while historians accepted at least 300,000 died, making it the deadliest earthquake in recorded history (excluding the famine deaths from the 1556 Shanxi earthquake) and one of the worst disasters in China by death toll.